Effect of process parameters of plasma electrolytic oxidation on microstructure and corrosion properties of magnesium alloys

In this work, a plasma electrolytic oxidation process was applied to AZ91 and AM50 magnesium alloys and commercially pure magnesium to produce a protective surface layer. The plasma electrolytic oxidation process was carried out in an alkaline phosphate solution with a DC power supply, using relatively high current densities and short treatment times. The influence of some important process parameters such as current density, treatment time and voltage was studied. The layers were characterised by scansion electron microscopy, X-ray diffraction and X-ray photoelectron spectrometry, in order to investigate the effect of the process parameters on the microstructure and chemical composition. The corrosion resistance properties of the obtained layers were investigated by potentiodynamic anodic polarization and electrochemical impedance spectroscopy tests. The current density, applied during the treatment, influenced the morphology and the thickness of the coatings, and, consequently, the corrosion resistance. The corrosion tests evidenced that the layers obtained with plasma electrolytic process provided a good corrosion protection to the magnesium and magnesium alloys.     

Measuring secondary phases in duplex stainless steels

The use of duplex stainless steels is limited by their susceptibility to the formation of dangerous intermetallic phases resulting in detrimental effects on impact toughness and corrosion resistance. This precipitation and the quantitative determinations of the phases have received considerable attention and different precipitation sequences (σ phase, χ phase, and carbides) have been suggested. This study investigates the phase transformation during continuous cooling and isothermal treatments in commercial duplex stainless steel grades and the effects on alloy properties, and compares the most common techniques of analysis.     

On the priority vector associated with a reciprocal relation and a pairwise comparison matrix

We propose two straightforward methods for deriving the priority vector associated with a reciprocal relation, by some authors called fuzzy preference relation. Then, using transformations between pairwise comparison matrices and reciprocal relations, we study the relationships between the priority vectors associated with these two types of preference relations. Eventually, we show a brief example involving the newly introduced characterizations.     

Effects of selective breeding for infant rat ultrasonic vocalization on cardiac responses to isolation.

Heart rates (HR) and autonomic control of heart period (HP) during maternal separation and isolation were measured at postnatal days (P) 10 and 18 in rat pups selectively bred for high, low, and random rates of infant ultrasonic vocalization. P10 pups displayed no significant line differences in HRs, strong tonic basal sympathetic control of HP and little sympathetic reactivity to isolation, and no evidence of tonic baseline or phasic parasympathetic responses to isolation. At P18, during isolation and recovery, Low HRs were significantly higher compared with Random and High pups. High HRs were significantly higher compared with the Random line in the last third of isolation and through recovery. The higher HRs of Low pups during stress were due to greater parasympathetic withdrawal, but greater sympathetic activation could not be ruled out. Higher HRs in High pups were due to increased sympathetic activation. Thus, increases in HR responses in the selected lines are due to different underlying autonomic processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

In-situ neutron diffraction study of magnesium amide/lithium hydride stoichiometric mixtures with lithium hydride excess

The hydrogen sorption of mixtures of magnesium amide (Mg(NH₂)₂) and lithium hydride (LiH) with different molecular ratios have been investigated using in-situ neutron diffraction; the experiments were performed at D20/ILL and SPODI/FRMII. The results reveal a common reaction pathway for 1:2, 3:8 and 1:4 magnesium amide: lithium hydride mixtures. Intermediate reaction steps are observed in both ab- and desorption. The thermodynamic properties of the system at 200 °C are not changed by the addition of excess lithium hydride. This finding has important implications for the tailoring the characteristics of this promising hydrogen storage material.     

Effect of the Heat Treatment on the Corrosion Resistance of Duplex Stainless Steels

Duplex stainless steels (DSS) are biphasic austenitic-ferritic steels in which the best combination of mechanical and corrosion resistance properties is achieved for an almost equal volume fraction of the phases. In this work, the effect of secondary phases precipitation on the corrosion resistance of four DSS grades (2101, 2304, 2205 and 2507), after isothermal aging in the critical temperature range 750-900 °C, was studied. The corrosion resistance was investigated by potentiodynamic polarization tests in both 0.6 M NaCl solution (pH 7) and in an acid chlorinated solution (pH 3) at room temperature. Moreover, the critical pitting temperature was determined according to ASTM G150. The results showed that secondary phases precipitation mainly influenced the resistance to corrosion of the lean duplex grades.     

Catalytic Regioselective Epoxide Ring Opening with Phenol Using Homogeneous and Supported Analogues of Dimethylaminopyridine

The regioselective ring opening of terminal epoxides using phenolic nucleophiles is examined using dimethylaminopyridine (DMAP) as a soluble catalyst and solid catalysts based on silica, polymer, and magnetic nanoparticle solids functionalized with DMAP analogues. The homogeneous reaction proceeds to 94?% conversion while achieving 93?% regioselectivity in 2?h at 120?°C. DMAP efficiently catalyzes the ring-opening reaction of a variety of epoxides using different substituted phenols with high conversions and excellent regioselectivities. Of the heterogeneous catalysts, the polymeric catalyst is more active and recyclable than the magnetic nanoparticle and silica supported catalysts, which had comparable activity and recyclability.